Milky spots in the greater omentum are predominant sites of local tumour cell proliferation and accumulation in the peritoneal cavity

The role that milky spots in the greater omentum play in tumour cell spread in the peritoneal cavity is presently not fully understood. To study wheth er intraperitoneally injected tumour cells appeal preferentially in milky s pots of the greater omentum and to study the changes in the greater omentum , and especially in the cell population of milky spots after tumour cell in filtration, the following study was performed. A detailed temporal sequence s of changes in morphology and cellular composition in milky spots of the g reater omentum of Wag/Rij rats 5, 15, 30, 60 min, 2, 4, 8, 16, 24 h. 2, 4, 8 days and 2 and 4 weeks after intraperitoneal administration of 2.0 x 10(6 ) CC 531 tumour cells was investigated by light microscopy and electron mic roscopy (pre-embedding labelling). Our data showed that the milky spots in the greater omentum were the sites to which tumour cells migrated preferent ially from the peritoneal cavity. The tumour cells infiltrated the milky sp ots and formed clusters within. The cellular population in milky spots reac ted by a very rapid influx of young macrophages during the first hour and a n increase of the total number of cells (P < 0.01). After 4 h tumour cells were also located on the greater omentum outside the area of the milky spot s. Around these tumour cell deposits, new milky spots are formed. which inc reased the total number of milky spots. The cells present in milky spots ar e not capable of reversing the growth of rumours and finally a solid omenta l cake of tumour cells is formed.